1. Field of Invention
The present invention relates to a scanning apparatus, more particularly to a scanning apparatus with heat dissipating ability.
2. Related Art
A scanning apparatus is composed of a housing, a light emitting unit, and an image scanning module. The light emitting unit and the image scanning module are disposed in the housing. The light emitting unit is provided for emitting a scanning light onto a document through a slit formed on the housing. The scanning light is reflected by the document to form an image light according to the image of the document, and the image light is then received by the image scanning module to be converted to an image data.
Generally in the prior art, a cold cathode fluorescent lamp (CCFL) is generally used as the light emitting unit to emit an ideal white with a uniform light intensity distribution. However, a high operating voltage and a high discharge voltage are required to activate the CCFL, so a high voltage driving circuit is required to be disposed in the scanning apparatus for providing a high voltage to drive the CCFL. Therefore, the cost of the scanning apparatus is increased. Moreover, after the CCFL is activated, a period of time is required before the intensity of the emitted light becomes stable. That is to say, after the scanning apparatus using the CCFL is turned on, it is necessary to wait for a period of time for warming-up the CCFL before the scanning apparatus is operated. Furthermore, the intensity of the light emitted by the CCFL is varied with the temperature of the CCFL. If the temperature of the CCFL increases after the scanning apparatus performs uninterrupted operation, the intensity of the emitted light may also change, and even the spectrum of the light shifts, such that the emitted light is not the ideal white light anymore, and the image scanning quality under the uninterrupted operation of the scanning apparatus is inconsistent.
Currently, the light emitting diodes (LEDs) have been widely applied to provide the scanning light, and through the arrangement of the LED array, the LEDs are made to generate the scanning light with a uniform light intensity distribution. Meanwhile, the LED is not limited to the white light LED capable of emitting the ideal white light, but for example, the ideal white light can be obtained by combining various LEDs which emits single color scanning lights such as red, green, and blue lights.
However, the LEDs generate a large amount of heat during emitting light, such that the application of the LEDs is limited. The heat generated by the LEDs negatively affects the other components in the scanning apparatus, and the scanning apparatus may be malfunctioned due to the heat generated by the LEDs. Take the negative effect on LEDs themselves as an illustration, the intensity and the spectrum of the light emitted by the LEDs are varied when the temperature of the LEDs rises to a critical temperature, and the image scanning quality is also negatively affected due to the variation of the intensity and the spectrum of the emitting light. Meanwhile, the rising temperature may also negatively affect the electro-luminescent material in the LEDs. The decay time of the electro-luminescent material in the LEDs is shortened, and the life span of the LEDs is also shortened. In addition, the circuit connected to the LEDs may be burnt out due to the affect of the high temperature.
In order to solve the problem caused by heat generation of the LEDs, the common solution is to reduce the quantity of the LEDs of a LED array and to enlarge the interval between two neighboring LEDs. However, this solution greatly reduces the intensity of the light emitted by the LED array, and makes the intensity distribution of the emitted light be non-uniform, so that the image scanning quality is also negatively affected.
As for dissipating heat generated by the LEDs, US Patent Publication No. US2006/0087828 (also disclosed as ROC Taiwan Patent No. TWM251986) provides a light-emitting diode lamp with high heat dissipation, which is used as the light source required by the scanning apparatus. US2006/0087828 includes a thermal conductivity cavity, a transparent cover, and a plurality of LEDs. The thermal conductivity cavity has a rectangular opening, and a reflective pattern is formed in the thermal conductivity cavity corresponding to the opening. The transparent cover is equipped to cover the opening of the thermal conductivity cavity, and the LEDs are disposed on one end or both ends of the thermal conductivity cavity to emit the scanning light, such that the scanning light is reflected by the reflective pattern to pass through the opening. However, in US2006/0087828, the LEDs horizontally emit the light, and then the light is reflected by the reflective pattern to the opening, such that the light intensity distribution uniformity along the opening is relatively poor. Therefore, the transparent material such as the epoxy resin is requires to be filled in the thermal conductivity cavity to act as the light-guide element, so as to improve the light intensity distribution of the LEDs. However, the transparent material, such as epoxy resin, is easily affected by the high temperature of the LEDs directly, as a result, the material is increasingly deteriorated to become non-transparent, and thus losing the light-guide ability, and directly blocking the lights emitted by the LEDs.